Elements of machine learning

The official title of this free book available in PDF format is Machine Learning Cheat Sheet. But it's more about elements of machine learning, with a strong emphasis on classic statistical modeling, and rather theoretical - maybe something like a rather comprehensive, theoretical foundations (or handbook) of statistical science. Anyway, very interesting, and it's free. See table of content screenshot below. Download free PFD copy (119 pages).

The chapters 17 to 28 (the most interesting ones in my opinion) seem like a work in progress - I'm sure the authors intend to make them a bit bigger. For a more modern and applied book, get Dr Granville's book on data science.